134 ELEMENTARY ZOOLOGY. 



binds them into permanent colonies, as in the corals. 

 Such colonies rarely occur among animals in which the 

 organs are highly specialized. Colonial animals are 

 almost always attached to fixed or to floating objects. 



FIG. 27. An organic colony of a fresh water polyzoan, Plumatella. After Allman. 

 stat, statoblasts, reproductive bodies. 



Question on the Figure. Evidences that this is a colony rather 

 than an individual. Where are the younger and where the older 

 individuals? How much constitutes an individual? What powers 

 of adapting themselves to the surroundings do these individuals 

 show? How are new individuals formed in the colony? How are 

 new colonies formed? 



Colonies are a successful device whereby limited areas 

 are completely occupied by the combined offspring of 

 one egg, where a single polyp would be well-nigh helpless. 



149. Practical Exercises. Study figures of colonies, in the refer- 

 ence books, and note their variety of form and size. What deter- 

 mines the shape which a colony takes? What phyla of the animal 

 kingdom furnish instances of colonies? Are the individuals of a 

 colony all alike? If not, what is the meaning of the differences? 

 How are new colonies started ? 



